1. Field of the Invention
The present invention relates to a light cable, and more particularly to a light cable for use in an apparatus for ophthalmic operation using photocoagulation by a laser beam.
2. Description of Related Art
Conventionally, there is an apparatus for ophthalmic operation using photocoagulation, which photocoagulates an affected part of a fundus of a patient's eye by applying a laser beam.
During the ophthalmic operation by photocoagulation using said apparatus as mentioned above, the ophthalmologist observes the patient's eye through the observing optical system, like an ophthalmic operation microscope, so that it is necessary to introduce the laser beam into the optical path of the observing system in the microscope.
Usually, an optical fiber is used to transfer the laser beam from the apparatus body which includes a laser system and its control system to a laser delivering system which includes optics which defines the irradiation area. The laser delivering system is attached to the observing system of the microscope to be optically coaxialized.
In one conventional method, the illumination system of the ophthalmic operation microscope is utilized. The optical axis of laser beam becomes coaxial with that of the observing system by means of installing a mirror which is positioned to reflect the laser beam to be coaxial with the optical axis of the observing system. However, in order that the optical axis of the illuminating system be inclined with about 4 degrees to the optical axis of the optical system for irradiating the laser beam, the illuminated visual field sometimes does not correspond with the range of movement of the laser beam, so that the laser beam irradiates out of the illuminated visual field.
In a second conventional method, the optical axis of the optical system for irradiating the laser beam is coaxial with the optical axis of the optical system for illumination, that is, the center of the optical system is occupied by the laser transmitting system and the circumference thereof, without interfering with the laser transmitting system, is occupied by the illuminating system.
However, when using the second method, it is necessary that a small mirror be arranged in the optical system, to adjust the two optical systems so as to be coaxial without interfering mutually. Thus, the optical system is complicated in this combination so that the adjustment of the optical system becomes difficult. Because of the apparatus becoming large in size, it is difficult to be installed in a simple type microscope.
Further, according to the second method mentioned above, the optical axis of the laser irradiating optical system and the optical axis of the illumination optical system are coaxial, but each beam is transmitted through separate space, and, depending on circumstances, only the illumination light is shut off before reaching the fundus of the patient's eye. As a result, a problem like that in the first method occurs.